First Sighting: DNA Double Helix

Researchers in the department of nanostructures and nanochemistry at the Genoa-based Istituto Italiano di Tecnologia (IIT) report that they have imaged the DNA double helix for the first time through an electron microscope. Working with colleagues at the University of Magna Grecia in Catanzaro, the team says it developed a method that allows them to stretch DNA filaments throughout the entire double helix structure on a silicon surface. This permits the investigators to directly image the helix by a transmission electron microscope.

The study of single molecules, or of small quantities of molecules, is important for the understanding of fundamental biological mechanisms at the nanoscale level. The technique developed at the Istituto Italiano di Tecnologia will allow to see how proteins, RNA, and other biomolecules interact with DNA. “Our research originated from the awareness that, to deepen the knowledge of the way DNA works, it is necessary to have new tools, allowing us to show in a direct way its structure and its functions, both in the coding and noncoding portions,” explains Enzo Di Fabrizio, coordinator of the study and director of the nanostructures department of IIT.

The researchers built a device made up of a silicon surface, with regularly spaced micropillars rising from it, interspersed by holes. The micropillars give the device the characteristic of super-hydrophobicity, while the holes allow the electrons to cross the sample to reach the microscope detector undisturbed, i.e., with no interaction with the silicon surface.

This experiment requires a very complex procedure: enclosing the DNA strands in a drop of solution; laying the drop on the device which, thanks to the micropillars, sustains its shape leaving the strands intact; allowing the solution to evaporate slowly and using the electron microscope to image the result. In particular, during the evaporation procedure, the connective movements inside the drop stretch the DNA strands, arranging them on the micropillars. At the end of the evaporation, DNA is then suspended between the micropillars and ready to be irradiated with the electron beam by the microscope.

The result has been obtained on strands made of six molecules, coiled around a seventh one. In the near future, the development of electron detectors 10–100 times more sensitive than those currently available will allow to directly image single and double DNA helices with the aim of studying directly both epigenetic phenomena and the information contained in the noncoding portions of DNA.